CZ432499A3 - Process and apparatus for electrochemical machining - Google Patents

Abstract

In the process, electrical impulses are introduced between the workpiece (2) being processed and the electrically conductive electrode (6), wherein one or more machining pulses (Mp) are alternating with voltage impulses (PP) to store passives layers on the workpiece being processed (2). Voltage Amplitude pulses (PP) is adjusted during the adjustment procedure, during the amplitude of the voltage pulses (PP) gradually increases from zero to the voltage at which the workpiece (2) starts dissolved in the electrolyte. Each time the voltage is increased, it is measured the gap resistance (5) between the electrode (6) and the workpiece (2). Value Voltage! is stored for the highest gap resistance (5) in memory and used during further machining. Time period voltage pulses (PP) can be divided into time for each time slot (Dt), the voltage is adjusted for maximum resistance during this time period (Dt). Equipment for electrochemical machining it comprises an electrode (6), means for positioning the electrode (6) a the workpiece (21) being processed to maintain the gap (5) between electrode (6) and workpiece (2) as well as power sources a control means.

Description

The invention relates to a method, apparatus and power source for electrochemical machining of a conductive workpiece by introducing electrical machining pulses between the workpiece and the electrically conductive electrode, wherein an electrolyte is fed between the workpiece and the electrode.

BACKGROUND OF THE INVENTION

Electrochemical machining is a method in which an electrically conductive workpiece dissolves at the electrode site while electrolyte and electrical current are supplied. For this purpose, an electrode is introduced near the workpiece and, at the same time as the electrolyte is introduced into the gap between the workpiece and the electrode, a high current is passed through the workpiece and the electrode, the workpiece being positive with respect to the electrode. The current is supplied in the form of machining pulses having a given amplitude and duration. The electrolyte is renewed at intervals between machining pulses. During the introduction of the machining pulses, the electrode and the workpiece move together at a given feed rate, as a result of which the electrode creates a cavity and possibly a hole in the workpiece surface. This process can be used, for example, to produce complex cavities or holes in the processing of hard metals and alloys.

The copying accuracy with which the shape of the cavity or hole in the workpiece follows the shape of the electrode is important for the quality of the result. A number of articles in the press and a number of patent documents have been published in which proposals for improvement have been submitted

• · ·

-2 copying accuracy in electrochemical machining.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method and apparatus for electrochemical machining that can be copied with good copying accuracy.

SUMMARY OF THE INVENTION

This object is achieved by a method of electrochemically machining an electrically conductive workpiece by introducing electrical machining pulses between the workpiece and the electrically conductive electrode, wherein an electrolyte is introduced between the workpiece and the electrode, the principle being that machining pulses alternate with electrical passivation pulses wherein the passivation pulse voltage has an amplitude that is insufficient to dissolve the workpiece and the passivation film on the workpiece.

At intervals between machining pulses, during electrolyte renewal, passivation pulses are introduced with intentional amplitude such that a passivation layer of metal oxides is formed around the electrode on the workpiece. During the next machining pulse, this layer is selectively removed at the end surface of the electrode. In this way, the machining pulse provides greater efficiency in the feed direction. This improves the copying accuracy, since comparatively more workpiece material dissolves at the end surface of the electrode, and smaller cavities are formed in the cavity to be formed in the workpiece at the edges and slopes of the side surface of the cavity. Another advantage to be noted is that the energy consumption of the process is less and the dissolution rate of the workpiece in the infeed direction is higher. This is because due to the local passivator ············

In the outer layers, the energy of the machining pulses is no longer used for unwanted removal of material from the side surfaces of the cavity in the workpiece.

Preferably, a distance is maintained between the workpiece and the electrode which is smaller during machining pulses than during passivation pulses. By increasing the distance between the workpiece and the electrode during passivation pulses, it is achieved that, due to the greater distance, the electric field of the passivation pulses has less effect at the end surface of the electrode than on the side walls of the cavity in the workpiece. It is thus achieved with great precision that a thinner passivation layer or even no passivation layer is formed against the end surface of the electrode, i.e. at the bottom of the workpiece cavity, than anywhere else in the cavity to be machined. The amplitude, duration and shape of the machining pulses are selected such that activation of the surface to be machined occurs only in the case of a small distance during the machining pulses. In such a case, the anode dissolves during machining pulses only at those locations in the workpiece where the gap is less than the critical distance. The rest of the workpiece is protected by a passivation layer and does not dissolve. This leads to very high copying accuracy. In a variant of the method according to the invention, the workpiece and the electrode exert a reciprocating movement, the distance between the workpiece and the electrode reaching a minimum during these machining pulses.

The amplitude of the passivation pulse voltage plays an important role. Too low a voltage has little or no effect because the passivation layers are too thin. Too high a tension, on the other hand, causes the previously formed passivation layers on the side surfaces of the cavity to disappear, causing deterioration in copying accuracy. On the other hand, an even higher voltage will result in the same effect as normal machining pulses and cause the workpiece to dissolve at various undesired positions in the machined cavity. In order to optimize the amplitude of the passivation pulses, a variant of the method according to the invention is characterized in that the amplitude of the passivation pulses in a series of successive passivation pulses changes until the resistance value measured between the object and the electrode has reached its maximum. pulse that corresponds to the maximum resistance value.

During a series of successive passivation pulses, the voltage amplitude of the passivation pulses gradually changes, for example increasing from zero to a given maximum value at which the workpiece begins to dissolve. At each subsequent passivation pulse a slightly higher voltage is applied and the gap resistance is measured and stored. From the measured resistance values, the highest value is selected and the corresponding voltage amplitude is fixed and held for a period of time during the subsequent machining of the workpiece. The voltage amplitude of the passivation pulses is thus optimized for maximum gap resistance. As a result, the formation of passivation layers on the side surfaces is also maximized and copying accuracy is optimal.

For this purpose, the device according to the invention comprises: an electrode;

means for positionally positioning the electrode and the workpiece in the space to maintain the gap between the electrode and the workpiece; means for introducing an electrolyte into the gap;

A first electrical power source that is electrically connectable to the electrode and the workpiece to deliver machining pulses to the workpiece and the electrode;

a second power source of the same polarity as the first power source and having an output voltage that is controllable by means of a control signal, the second power source being electrically connectable to the electrode and workpiece for supplying passivation pulses to the workpiece and electrode being processed;

means for alternately connecting the first power source and the second power source to the workpiece and electrode being processed;

means for generating a variable control signal for varying the output voltage of the second power source during successive passivation pulses;

means for measuring, during successive passivation pulses, the electrical resistance of the gap between the workpiece and the electrode at a time during passivation pulses, and for storing resistance information values that are representative of the gap resistance at this time and for storing corresponding control signal values at that time ; and means for calculating the maximum value from the resistance information values, and means for maintaining the control signal for the second power source at the control signal value that corresponds to the maximum value.

The second power source is controllable and the voltage gradually increases, and the voltage value for which the measured gap resistance is maximum is stored.

When a variable gap distance is used, •

-6 Any value of the distance between the workpiece and the electrode corresponds to a different optimal amplitude of the passivation pulse voltage. This is particularly the case when the workpiece and the electrode perform an oscillating movement relative to each other, and the distance between them is therefore never constant. In order to avoid this problem, a further variant of the method according to the invention is characterized in that the passivation pulses are divided into periods and the instantaneous amplitude of the voltage of the passivation pulses changes for each individual period until the resistance measured between the object and the electrode has reached The electrochemical machining proceeds with passivation pulses, the instantaneous amplitude of which varies according to the amplitude found for each period and corresponds to the maximum value of the resistance in that period.

The time course of each of the passivation pulses is divided into a plurality of time intervals, and in each time period the voltage amplitude changes during successive passivation pulses until a maximum resistance is found in that time period. The corresponding optimal passivation pulse voltage over this period of time is stored. Upon completion of this adjustment procedure, all stored optimized slots are successively generated in the correct sequence over time passivation pulses, as a result of which the passivation pulse voltage amplitude has a shape that is optimized for gap size variation.

For this purpose, an embodiment of the device according to the invention is characterized in that the means for generating a variable control signal comprises means for varying the output voltage of the second power supply source at different times.

9 99

- during the time period of one passivation pulse;

wherein the measuring and storing means is adapted to store resistance information values that are representative of instantaneous gap resistance at different moments in the passivation pulse and for storing corresponding values of the control signal at different moments;

and the calculating means is adapted to calculate individual maximum values from resistance information values at respective moments in successive passivation pulses and to generate a control signal having an instantaneous value equal to control signal values corresponding to individual maximum values at different moments. .

Thus, the voltage of the second power source varies over the time course of the passivation pulse, the shape of which is best suited to the changing gap size during the passivation pulse.

The above adjustment procedure for determining and maintaining an optimum waveform for passivation pulse voltage can be repeated as often as necessary during further electrochemical machining of the workpiece.

A variant of the method according to the invention is characterized in that, at intervals between successive machining pulses, additional electrical pulses of opposite polarity are introduced between the workpiece and the electrode having a voltage whose amplitude does not exceed the amplitude at which the electrode begins to dissolve in the electrolyte. in time intervals between ·· • · • ·

After successive machining pulses, the passivation pulses alternate with electrical pulses of opposite polarity, the latter having a voltage whose amplitude does not exceed the amplitude at which the electrode begins to dissolve in the electrolyte.

The method is now replenished and / or alternates with electrical pulses of opposite polarity at intervals between machining pulses. The purpose, effect and adjustment of the voltage amplitude of pulses of opposite polarity are comprehensively described in International Patent Application WO 97/03781. This application describes between which optimal pulse voltage amplitudes of opposite polarity can be adjusted to prevent the electrode from dissolving and thereby reducing machining accuracy, and second, to achieve high machining efficiency in combination with a well-defined surface condition, e.g. a certain shine. When machining chrome-nickel steel, it is found that under these operating conditions, the concentration of hexavalent toxic chromium remains in the final electrolyte solution, making it easier to comply with environmental protection requirements.

The gap resistance can be calculated by measuring the current and voltage before the gap between the electrode and the workpiece and storing the measured data in memory. The current and voltage are preferably measured by means of analog-to-digital converters connected to a computer in which the measured data is stored. The computer calculates the maximum gap resistance by analyzing the measured data. The computer further generates a control signal for controlling the output voltage of the second power source. During the serialization process, the output voltage of the second power source gradually changes as the controller controls it.

signal from the computer. After the computer has detected the maximum resistance value, the corresponding control signal is continuously generated by the computer over a given period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a diagram of an embodiment of an apparatus for carrying out the method according to the invention; FIG. 2 shows the waveforms of the signals used in one embodiment of the method according to the invention; FIG. 4 shows the waveform of an electrolyte between the electrode and the workpiece when carrying out a variant of the method according to the invention; FIG. 7 shows a diagram of the formation of passivation layers in a machining cavity of a workpiece when carrying out a variant of the method according to the invention; FIG. 8 shows the shape of the voltage and resistance between the electrode and the workpiece when carrying out a variant of the method; 9A and 9B 10 shows the waveforms of the additional signals that occur in the variant of the method of the invention and FIG. 11 the waveforms of the additional signals that occur in another variant of the method of the invention. In these drawings, parts having the same function are designated with the same reference numerals.

DETAILED DESCRIPTION OF THE INVENTION

1 shows an apparatus for electrochemical machining of a workpiece 2 to be processed. The workpiece 2 is mounted on a table 4, which is conveyed at a conveying speed to the electrode 6, executing 10000

I 0 0 4

I 0 0 <

-1000 0 «> 1 0

000 oscillating movement with respect to the workpiece 2 provided by the crankshaft 8 driven by the motor 10. For example, the workpiece is of chromium-containing steel. In the gap 5 between the workpiece and the electrode 6, an electrolyte flows, for example in the form of an aqueous alkali metal nitrate solution, and circulates under pressure Iq from the tank 2. Workpiece 2, table 4 and electrode 6 are electrically conductive. The electrode 6 and the table 4 are connected to a power source 12 that supplies electrical pulses to the electrode 6 and the table 4. The electrical pulses comprise machining pulses having a polarity for which the table 4 and hence the workpiece 2 are positive relative to the electrode and of the workpiece 2, wherein these pulses alternate with passivation pulses having the same polarity but voltage and shape as described below. During the machining pulses, the metal of the workpiece 2 enters the anode dissolution in the electrolyte. During passivation pulses, the workpiece surface 2 is locally passivated.

In Fig. 2, curve I shows the magnitude S (t) of the gap between the electrode 6 and the workpiece 2. Curve II in Fig. 2 shows voltage variations across gap 5 during the adjustment procedure described below and curve III shows voltage across gap 5 during the following machining process. The machining pulses are applied at the time interval t1 shown in curve IV in FIG. 2, in which the electrode 6 is closest to the workpiece being processed 2. During these machining pulses, the voltage across the gap 5 has a waveform with a global minimum as indicated in the curve II in FIG. The machining pulses alternate with the PP passivation pulses at the same time interval tu. 2. It should be noted that the shape diagrams of the stress U through the gap 5 shown are only

· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·

-11 with an approximate representation of the actual shape curves.

Figure 3 shows schematically the processes that occur in the gap 5. In the initial stage of approach of the electrode 6 to the workpiece 2 in the case of a comparatively large space ^{with 3} and a maximum P ^roud electrolyte turbulent nature and the electrolyte contains vapor and gas bubbles. At this stage, the space between the electrode 6 and the workpiece has a relatively high electrical resistance, as can be seen from the first maximum in voltage U on curve II in Fig. 2. As the electrode 6 approaches, the pressure in the electrolyte rises and the gas bubbles dissolve, making the electrolyte homogeneous and uniform in the gap and a high current density at a small gap size can be achieved in the gap. As a result, the electrical resistance decreases, which is evident from the occurrence of the global minimum at voltage U in curve II of Figure 2.

Due to the increase in the distance between the electrode 6 and the workpiece 2 and again triggered by the formation of steam and gas bubbles, the electrical resistance again increases to the second maximum shown in curve II in Fig. 2. The electrical power supply can be so large that the electrolyte starts to boil heavily and cavitation occurs in the gap. Cavitation causes a temporary increase in the electrical resistance of the electrolyte, which results in a temporary increase in the voltage variation U between the electrode and the workpiece during machining pulses.

Figure 4 shows in greater detail the voltage change U with the voltage local maximum U3max that occurs after the global minimum Umin. It should be noted that such strong cavitation can be eliminated by developing groups of machining pulses that alternate with passivation pulses. Such

-12Φ * φ * φ * φ ·· ·· φ φ φ φφφφ φ φ φ φ φ φ φ φ φ φ · φ φ · · · φ φ φ φ φ φ φ φ φ znázor znázor . Thus, the process works with greater stability and more accurate results using the same minimum gap size.

Fig. 6 shows an electrical block diagram of a machining apparatus according to the invention comprising an electrical power supply 12 according to the invention. The electric power supply 12 comprises a machining current supply 14 providing a current I, the magnitude of which is controlled by the control signal CSI, and a controllable voltage source 16 for supplying the passivation pulses, the voltage source 16 providing an output voltage Up which is controllable CSU signal.

The negative terminal of the current source 14 and the negative terminal of the controllable voltage source 16 are both connected to the electrode 6 via a series resistor 18. The positive terminal of the current source 14 is connected to the workpiece 2 via switch 20. The switch 20 is switched on at intervals t1. The positive terminal of the controllable voltage source 16 is connected to the workpiece 2 via the switch 24. The switch 24 is switched at time intervals tu (Fig. 2) under the control of the signal Su, which is also powered by the synchronization unit

The analog voltage U between the electrode 6 and the workpiece 2 is measured at terminals 32 and 34 and is converted to a digital signal DU stored, analyzed and in the computer 28.

The gap current I is measured by dropping the voltage across the series resistor 18 at terminals 36 and 38 by means of a second

-13φ * φφ · φφ · • φ · · · · φ φ φ φ φ φ φ φ φ · · · φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ a converter 30 that converts the analog voltage drop to a digital signal DI, which is processed by the computer 28 similarly to a digital signal DU. Instead of a series resistor 18, a conventional transformer or any other suitable interface may be selected. The analog-to-digital converter 30 can be omitted if, at appropriate times, the converter terminals of the digital converter 26 are switched from voltage measurement, via terminals 32 and 34, to current measurement using terminals 36 and 38.

The synchronization unit 22, the analog-to-digital converters 26 and 30, and the computer 28 are powered by clock pulses (not shown in FIG. 6) which ensure that data acquisition and data processing are synchronized with alternating machining and passivation pulses and electrode oscillation. The position of the table 4 is monitored by a position sensor 40 which provides a signal DS that is a measure of the displacement of the table 4. The computer 28 generates a control signal CSI for the power source 14 and a control signal CSU for the controllable voltage source 16 via suitable interfaces 42 and 44. designed as digital-to-analog converters. The angle of rotation of the crankshaft 8 is measured by a sensor 46 that provides a DP signal to the computer 28 which is a measure of the relative distance between the electrode 6 and the workpiece 2.

By controlling the speed Vk of the table 1, the gap 5 can be adjusted to produce a local maximum U 3 max, as shown in Fig. 4. This local maximum can be detected by analyzing the voltage U by the analog-to-digital converter 26 and the computer 28 or by using an oscilloscope. However, any other working point for the me-14 • 9 · 9 99 size can be selected if necessary

9 9 «

9 9 9 9 9

9

9 9 9 9 9

9 · 9 9 9

9 9 9 9 9 9 zery 5, i.e. one in which there is no local maximum U3max at the voltage U.

7 shows the effect of passivation pulses. The voltage amplitude Up of the controllable voltage source 16 is selected such that it forms passivation layers PL in the machined cavity in the workpiece. However, the amplitude of the voltage Up is not so high that the workpiece dissolves or the passivation layers dissolve again. Due to the oscillating movement, the distance d_2 between the end surface of the electrode 6 during the machining pulses is less than the distance d1 between the side wall of the machining cavity and the electrode 6. If the amplitude and duration of the machining pulses are correctly selected ie against the end surface of the electrode 6 in the feed direction and not in the position of the passivation layers PL. This results in a very good copying accuracy and in that the shape of the cavity in the workpiece 2 very closely follows the shape of the electrode 6. Complex profiles and slopes of recesses or holes can be achieved with an accuracy of 10 arc minutes. Locally applied passivation layers ensure not only higher machining accuracy but also better energy efficiency and higher machining speed. This is because no energy is wasted on unwanted removal of material from the side walls of the machining cavity.

For optimum effect, it is therefore desirable if the voltage of the passivation pulses has an amplitude that is not so large that the passivation layers PL or even the workpiece itself dissolve and which is not so small that sufficient or barely any passivation layers. In both cases, the machining pulses will dissolve the workpiece 2 wherever possible and will create a relatively larger machining cavity in all

-15flfl ·· flfl · flfl ·· «• fl fl» fl flflflfl • • flfl fl * * flfl * flfl flflfl · · flfl flflfl flflfl flflflfl • flflfl · «flfl« flfl flfl * the copying accuracy is reduced. The optimal amplitude of the passivation pulses is the amplitude for which the gap resistance 5 is highest. This is because the growth of the passivation layers PL having low electrical conductivity is then maximized and the copying accuracy is also maximized.

To achieve optimal adjustment of the passivation pulse voltage amplitude, the electrochemical machine tool (Fig. 6) induces an adjustment procedure in which the passivation pulse voltage Up is increased in steps from 0 V to Uap, where the workpiece 2 enters the anode solution during successive oscillations. For this purpose, the computer 28 applies a suitable control signal CSU to the controllable voltage source 16 via the interface 44. After each increase in voltage Up, the resistance of the gap 5 is measured by analog-to-digital converters 26 and 30. The measured resistance value and the corresponding control signal are stored. as the numerical values in the main memory of the computer 28. Of all the resistance values found, the computer determines the largest value of the associated voltage amplitude Up.

The adjustment procedure is now complete, and for a given period of time TM, the machining process continues using the voltage thus found Up. As a result of the oscillating movement of the electrode 6, the distance between the workpiece 2 and the electrode 6 in the conveying direction will change continuously during the passivation pulses. Each value of the distance between the workpiece to be processed and the electrode corresponds to a different optimal amplitude of the passivation pulse voltage. To enable this, the passivation pulse time period is divided into periods of time. The optimum amplitude for each time period is now determined, with the gap resistance being at this time-16. ** · · «* · maximální maximální maximální maximální maximální maximální maximální maximální maximální maximální maximální maximální maximální maximální maximální Upon completion of the adjustment procedure, the computer 28 leads such a series of control signals to a controllable voltage source 16 over the time period of each passivation pulse that the amplitude of the passivation pulse is supplied with a deflection that is optimal for varying gap size. An example of such a variable amplitude of passivation pulses is provided by curve III in Fig. 2. This sophisticated adjustment procedure will now be described in more detail with reference to the graphs shown in Fig. 8 and the flowchart of Figs. 9A and 9B.

In Fig. 8, curve I shows the distance S between the workpiece 2 and the electrode 6. The rotation of the crankshaft produces a sinusoidal displacement of the distance S, which reaches the minimum Smin during the machining pulses MP. Each rotation of the crankshaft 8 corresponds to a period with a period T. The adjustment procedure covers a group m of oscillations and thus has a duration mT. The adjustment procedure, i.e. the group of oscillations m, is followed by the machining period TM, in which the workpiece is further machined by the machining pulses MP and the passivation pulses PP having the amplitude deviation determined in the previous adjustment procedure. The length of the TM machining period depends on the working conditions and can be adjusted as required.

After the TM machining period is completed, the adjustment procedure is repeated, which is covered with oscillations. The number of times the adjustment procedure is repeated also depends on the operating conditions and the desired result. In the simplest case, the adjustment procedure is performed only once and the workpiece is electrochemically machined in a single machining operation in a subsequent machining process. Each group has a sequence number i from 1 to the value of the determined total time length of the machining process. Each

In addition, each oscillation, i.e. also the oscillations in the machining period TM, is divided into periods of length Dt. Each time slot has a sequence number k from 1 to n. In Fig. 8, each passivation pulse was divided into 8 time zones, i.e. n = 8, but apparently more or less time periods are also possible. The number of slots depends on the size and time change in relative movement between the workpiece and the electrode. A greater number of time periods leads to an increase in the resolution, with which the optimum shape of the amplitude of the passivation pulse voltage is determined, and an increase in copying accuracy.

The curve II in Fig. 8 shows a stepwise increase in the amplitude of the passivation pulses. At j = 1, the first step starting from zero volts is performed. For all time periods from k = 1 to k = n, the steps are the same. Further, the penultimate oscillation with the sequence number j = m-1 and the last oscillation with the sequence number j = m are shown. At the last oscillation having the sequence number j = m, the voltage amplitude is equal to the voltage Uap at which the workpiece is subjected to anode dissolution. After each period k (k = l ... n), the gap resistance R is measured and stored in the computer memory. In addition, the corresponding CSU control signal value is stored as a digital value. These n resistance measurements are repeated for each oscillation j (j = 1 ... m) and the result is shown on curve III, which shows the resistance values for each time period.

The maximum resistance Rmax in a series of m measurements is determined for each time period. As an example, it was assumed that the resistance values per time period measured at the penultimate oscillation having the sequence number j = m-l are also the values of the maximum »φ • φ

Φ Φ φ φ φ φ φ φφφφ

-18φφφφ φφ φφ · resistance Rmax (j = m-1, k = 1) to Rmax (j = m-1, k = n) for each time period. However, this is not necessary. The maximum gap resistance for each individual time period k can be determined in oscillations having a different sequence number 1. The computer knows the value of the corresponding CSU control signal for each value found for the maximum resistance Rmax. Upon completion of the adjustment procedure, i.e. in the machining period TM, the computer generates corresponding values of the control signal CSU in the correct sequence over the time period of each passivation pulse. The curve IV in Fig. 8 provides an example of the voltage variation U across the gap in the machining period TM.

The machining process and the adjustment procedure are performed in the manner shown in the flowcharts of FIGS. 9A and 9B. The blocks in these figures have the following designations:

BO: beginning Bl: i = 1 B2: U * _k ^{= 0} , k = 1 ... n B3: R * _k = 0, k = 1 ... n B4: ^u kli = ^{k =} 1 ·· -n B5: j = i B6: check DP close switch 20, open to generate a machining pulse switch 22 B7: k = 1 B8: ^u kji = < ^u kji ^{+ du)} < ^{U and} P open switch 20, close switch 22 B9: wait Dt BIO: measure I _to her Bil: ^R kji ⁼ Ukji / ^ kji B12: ^R kji> ^R * k ^?

B13: ^R * k “ ^R kji B14: ^U * k = ^u kji B15: k = k + i B16: k> n? B17: j = j + i B18: j> m? B19: ECM (U * _R , TM) B20: i = i + 1 B21: stop ECM? B22: end

In the BI block, both the sequence number and group are set to the initial value. In block B2, the individual optimal voltages U are set to zero for all times k. In block B3, all individual maximum resistance values R for all k slots are set to an initial value of zero. In block B4, the initial amplitudes of the passivation pulses to be incremented are set to zero for all k slots. In block B5, the counter j, which monitors the number of elapsed oscillations, is set to an initial value of 1.

After this initialization, the machining process begins. Block B6 checks the DP signal, which indicates the position of the electrode. In the correct position, the current source 14 is connected by closing the switch 20 and the controllable voltage source 16 is disconnected by opening the switch 24. Then, a machining pulse is generated and applied. This machining pulse has a given duration, which is also determined by a computer. After the machining pulse is complete, the slice counter k is set to 1 in block B7.

In block B8, the amplitude Ukj is in the k-th time slot

00 00 0 9 9 00 00 000 9 9 9

9999 9 9 · 0

000 0 0 0 0 00

0 0 0 0 · 000 0000 00 00

The -20j-th oscillation of the i-th group of the passivation pulse increments the value of the step dU. The resulting amplitude should not exceed the voltage Uap. In addition, the current source 14 is disconnected by opening the switch 20 and the controllable voltage source is connected by closing the switch 24. Then, in block B9, the waiting time of one period Dt of the time period is observed. Thereafter, the instantaneous current value is measured in the BIO block and stored in the k-th period of the j-th oscillation of the i-th group. In block Bil, the instantaneous resistance value is calculated by dividing the instantaneous voltage by the instantaneous current ^I kji ·

In block B12, it is checked whether the instantaneous resistance value R 1 thus formed is higher than the individual maximum resistance value R * _{to the} time slot. If this is not the case, a jump to block B15 is performed. If this value is higher, the individual maximum value of resistance R _k is _made equal to the instantaneous value of resistance R1, which is performed in block B13. In addition, in block B14, the corresponding individual optimum voltage U * for this period of time equal to the instantaneous value U _k j j is made. In block B15 it is investigated whether the number of k counted time slots is greater than n. current, the resistance is calculated and the maximum resistance value is assigned with the instantaneous voltage value. This continues until all the time passes.

Once all time slots have been completed, the number i of the vibration in block B17 is incremented by one and compared with the value of m in block B18. If the number of oscillations that have elapsed is less than or equal to m, the program returns to block B6 and returns

-21 • ♦ »·« the next machining pulse and in the next passivation pulse the voltage is incremented by one step. This continues for m oscillations. Thereafter, in block B20, the electrochemical machining process continues with individual optimal voltages U * _k (k = l ... n) over time periods during the TM period.

Then, in block B20, the group counter i is incremented with ol. In block B21 it is decided whether the machining process lasted long enough. If the machining process is to be continued for an extended period of time, the counter and groups must be incremented before a stop decision is made. The criterion for stopping the mechanical process can be, for example, the displacement of the table 4 by the DS signal of the position sensor 40 or the elapsed time of the process. If the machining process has not yet been completed, a return to block B2 follows and a new adjustment process begins, followed by another machining period TM. When the final value is reached, the machining process ends in block B22.

The method and apparatus described were used for machining a test sample. The sample and electrode material was 40X13 steel in the annealed state, the machining area was 2 cm ² and the electrolyte was 8% NaNO 3. During the machining process the voltage of the machining pulses was 7 V, the duration of the machining pulses was 2 ms, the electrolyte pressure near the inlet gap was 350 kPa, the electrolyte temperature was 18 ° C, the electrode oscillation frequency was 47 Hz and the oscillation amplitude was 0.2 mm . The passivation pulse voltage was +2.8 V for the minimum gap and +3.8 V for the maximum gap of +3.8 V.

Analysis of machining results showed that in comparison

with conventional machining methods, the use of the electrochemical machining of the invention provides an increase in machining productivity of 1.25 times and a reduction in energy consumption of 1.2 times. The electrode copy error to the surface to be machined was not greater than 0.01 mm.

If desired, the passivation pulses in curve III of Figure 2 and curve IV of Figure 8 may be supplemented and / or alternated with electrical pulses of opposite polarity. The purpose, effect and adjustment of the voltage amplitude of pulses of opposite polarity are comprehensively described in International Patent Application WO 97/03781. This application describes between which optimal limits the pulse voltage of opposite polarity pulses should be adjusted to prevent, on the one hand, the electrode from dissolving, thereby reducing machining accuracy, and, on the other hand, achieving high machining efficiency in combination with a well defined surface condition, for example in the form of a certain gloss. In a number of aspects, the arrangement of said international patent application is similar to that shown in Fig. 1a. However, to generate voltage pulses of opposite polarity at intervals between machining pulses, the polarity of the controllable voltage source 16 (Fig. 6) should be temporarily reversed, or an additional source of opposite polarity should be used as well as an additional switch comparable to switch 24.

The curve II in Fig. 10 shows how the machining pulses alternate with the negative voltage pulses. Instead of positive passivation pulses, negative pulses are now supplied which give the workpiece a high gloss. Negative voltage pulses can be applied before, during, or • •

after completion of the machining process described above.

Fig. 11 shows an alternative in which, at intervals between machining pulses, a negative voltage pulse is first applied, followed by a positive passivation pulse, whose shape and amplitude are determined according to the above-described adjustment procedure.

It has hitherto been assumed that the electrode and the workpiece exert an oscillating movement relative to each other, with a machining pulse being applied within the smallest distance between the workpiece and the electrode. As the distance increases, the possibility of electrolyte recovery is facilitated. Strictly speaking, however, such a change in distance is not necessary if the working conditions and the desired result allow it.

Instead of a rotating crankshaft, other drive mechanisms may be used to generate an oscillating or other movement to vary the distance between the electrode 6 and the workpiece 2. For this purpose, an electrically or hydraulically driven construction with a gear and a rack can be used, or an electrically or hydraulically driven guide screw. The electrode 6 can then be adjusted to abut the workpiece 2 after its size has been adjusted. During the machining process, the size of the gap is adjusted so that an essentially constant feed rate is achieved which is substantially equal to the dissolution rate of the workpiece 2 to be processed.

Claims (12)

Method for the electrochemical machining of an electrically conductive workpiece (2) by introducing electrical machining pulses between the workpiece (2) and the electrically conductive electrode (6), wherein an electrolyte is applied between the workpiece (2) and the electrode (2), alternating with the electrical passivation pulses of the same polarity as the machining pulses, the passivation pulse voltage having an amplitude that is insufficient to dissolve the workpiece (2) and the passivation film on the workpiece (2). Method according to claim 1, characterized in that the amplitude of the passivation pulse voltage is adjusted at least once during electrochemical machining, wherein the amplitude of the passivation pulses in a series of successive passivation pulses varies until the resistance value measured between the object (2) and the electrode ( 6), reached the maximum and then the electrochemical machining is continued with the passivation pulse amplitude corresponding to the maximum resistance value. Method according to claim 2, characterized in that the passivation pulses are divided into periods and, for each individual period, the instantaneous amplitude of the voltage of the passivation pulses changes until the value of the resistance measured between the object (2) and the electrode (6) has reached the electrochemical machining proceeds with passivation pulses, the instantaneous amplitude of which varies according to the amplitude detected for each period and corresponds to the maximum value of the resistance in that period. -254. Method according to claim 1, 2 or 3, characterized in that a distance is maintained between the workpiece (2) and the electrode (6), which is less during machining pulses than during passivation pulses. Method according to claim 4, characterized in that the workpiece (2) and the electrode (6) perform an oscillating movement with respect to each other, wherein the distance between the workpiece (2) and the electrode (6) reaches a minimum during machining pulses. Method according to any one of claims 1 to 5, characterized in that, at intervals between successive machining pulses, additional electrical pulses of opposite polarity are introduced between the workpiece (2) and the electrode (6) having a voltage whose amplitude does not exceed amplitude wherein the electrode (6) begins to dissolve in the electrolyte. Method according to any one of claims 1 to 5, characterized in that at intervals of successive machining pulses, the passivation pulses alternate with electrical pulses of opposite polarity, the latter having a voltage whose amplitude does not exceed the amplitude at which the electrode (6) begins to dissolve in the electrolyte. An apparatus for electrochemical machining of an electrically conductive workpiece (2) by introducing electrical machining pulses between the workpiece (2) and the electrically conductive electrode (6), while an electrolyte, characterized in that it comprises: : an electrode (6); means (4, 40) for positionally positioning the electrode (6) and the workpiece (2) in the space for maintaining a gap (5) between the electrode (6) and the workpiece (2); means (3) for introducing an electrolyte into the gap (5); a first electrical power source (14) electrically connectable to the electrode (6) and the workpiece (2) for supplying machining pulses to the workpiece (2) and the electrode (6); a second power source (16) of the same polarity as the first power source (14) and having an output voltage that is controllable by a control signal (CSU), the second power source (16) being electrically connectable to the electrode (6); a workpiece for supplying passivation pulses to the workpiece (2) and the electrode (6); means (20, 24) for alternately connecting the first power source (14) and the second power source (16) to the workpiece (2) and the electrode (6) to be processed; means (28, 44) for generating a variable control signal for varying the output voltage of the second power source (16) during successive passivation pulses; means (18, 30, 26, 28) for measuring, during successive passivation pulses, the electrical resistance of the gap (5) between the workpiece (2) and the electrode (6) at the moment during the passivation pulses and storing resistance information that they are representative of the gap resistance (5) at this point and for storing the corresponding control signal (CSU) values at this point; and means (28) for calculating the maximum value from the resistance information values, and means (28, 44) for maintaining the control signal (CSU) for the second power source (16) per value ** -27th control signal that corresponds to the maximum value. Apparatus according to claim 8, characterized in that the means (28, 44) for generating the variable control signal comprise means for varying the output voltage of the second power supply source (16) at different times during the time period of one passivation pulse; wherein the measuring and storing means (18, 30, 26, 28) is adapted to store resistance information values that are representative of the instantaneous resistance of the gap (5) at different times in the passivation pulse and to store corresponding values of the control signal at different times ; and the calculating means (28) is adapted to calculate individual maximum values from resistance information values at respective moments in successive passivation pulses and to generate a control signal having an instantaneous value equal to the control signal values at different times corresponding to individual maximum values. Device according to claim 9, characterized in that it further comprises means (8, 10) for varying the distance between the electrode (6) and the workpiece (2), which is smaller during the feeding of machining pulses than during the feeding of passivation pulses. Apparatus according to claim 10, characterized in that it comprises means (8, 10) for exerting oscillating movement between the workpiece (2) and the electrode (6), and means (22) for synchronizing means (20, 24) for alternately connecting the first a power source (14) and a second power source (16) with a power supply (16); - 28 - by melting the workpiece to be processed (2). An electrical power source for use in a method of electrochemically machining an electrically conductive workpiece (2) by introducing electrical machining pulses between the workpiece (2) and the electrically conductive electrode (6), while an electrolyte is supplied between the workpiece (2) and the electrode (6). characterized in that the electrical power source comprises a first electrical power source (14) which is electrically connectable to the electrode (6) and the workpiece being processed to supply machining pulses to the workpiece (2) and the electrode (6), a second electrical power source (16) power of the same polarity as the first power source (14) and having an output voltage that is controllable by a control signal (CSU), the second power source (16) being electrically connectable to the electrode (6) and the workpiece (2) being processed for feeding passivation pulses to the workpiece (2) and the electrode (6); means (20, 24) for alternately connecting the first power source and the second power source to the workpiece (2) and the electrode (6) to be processed; means (28, 44) for generating a variable control signal (CSU) for varying the output voltage of the second power source (16) during successive passivation pulses; means (18, 30, 26, 28) for measuring, during successive passivation pulses, the electrical resistance of the gap (5) between the workpiece (2) and the electrode (6) at the moment during the passivation pulses, and for storing resistance information, which are representative of the gap resistance (5) at this point and for storing the corresponding control values * · ·· 00 • · 0 0 «· * -29 · · · 0 · signal at this time; and means (28) for calculating the maximum value from the resistance information values, and means (28, 44) for maintaining the control signal (CSU) for the second power source (16) at the control signal value corresponding to the maximum value. The electrical power source of claim 12, wherein the variable control signal generating means (28, 44) comprises means for varying the output voltage of the second power supply source (16) at different times during the time period of one passivation pulse; wherein the measuring and storing means (18, 30, 26, 28) is adapted to store resistance information values that are representative of the instantaneous resistance of the gap (5) at different times in the passivation pulse and to store corresponding values of the control signal at different times ; and the calculating means (28) is adapted to calculate individual maximum values from the resistance information values at respective moments in successive passivation pulses and to generate a control signal having an instantaneous value equal to the control signal values at different times corresponding to individual maximum values.